This invention relates to a vacuum melting system, and more particularly, to a system for melting and vacuum refining metals.
Vacuum induction melting has been widely used for producing high performance metals and alloys. Typically, the melting takes place in a refractory-lined electric induction furnace located within a vacuum chamber. The furnace is charged with raw materials, then heated under vacuum until the raw materials reach a molten state and volatile impurities are refined from the melt. Then the furnace is typically tilted to pour the molten metal into one or more molds positioned for receiving the molten metal. The physical handling of the furnace and the successive heating and cooling cycles result in wear or damage to the refractory lining, with the result that it is necessary periodically to remove the induction furnace from the vacuum chamber and to repair or replace the refractory lining. This results in downtime and loss of productivity while the furnace is being removed for rebuilding and replaced by a rebuilt furnace. Also, it is sometimes necessary to replace the furnace to avoid contamination when changing to the production of a different alloy.
Many of the commercially available vacuum induction melting systems are operated on a batch-wise basis, with the vacuum chamber being opened after each melt so that the furnace can be recharged with raw materials, and other components, such as the tundish or launder can be replaced or rebuilt. Vacuum induction melting systems have been proposed which allow the vacuum melt chamber to be isolated from other chambers, for example the mold tunnel, so that filled molds can be removed and replaced by empty molds. Nonetheless, these systems are limited in their capability for being operated for extended periods of time in a continuous or semi-continuous manner.
The present invention provides a vacuum induction melting system which is designed to reduce downtime and to facilitate operation in a continuous or semi-continuous manner for extended periods of time to thereby significantly increase the efficiency of the melting system. The vacuum induction melting system of the present invention is also designed to make it possible to easily and quickly remove the induction furnace from the melt chamber when it becomes necessary to replace and rebuild the furnace.
The vacuum induction melting system of the present invention includes a melt chamber which forms an airtight enclosure, with an induction furnace located within the melt chamber. A charging chamber is communicatively connected to the melt chamber adjacent its upper end. The charging chamber includes a door providing access to the interior of the charging chamber so that a charge of raw materials can be placed therein. An isolation valve is located between the melt chamber and the charging chamber and is movable between open and closed positions. In the closed position, the charging chamber is isolated from the melting chamber to allow for loading of raw materials into the charging chamber through a door provided in the charging chamber. In the open position, the charging chamber is in communication with the melt chamber to permit adding the charge of raw materials to the induction furnace. A mold tunnel is connected to the melt chamber adjacent its lower end, with the mold tunnel including a pour opening which communicates with the melt chamber and through which molten metal poured from the furnace can enter the mold tunnel. A mold carriage is positioned within the mold tunnel for receiving and carrying one or more molds adapted for receiving molten metal. An isolation valve is located between the melt chamber and the mold tunnel and is movable between an open and a closed position. In the closed position, the mold tunnel is isolated from the melt chamber to allow for removing the mold carriage from the mold tunnel for loading or unloading of molds thereon. In the open position, the mold tunnel is in communication with the melt chamber so that molds can be filled with molten metal. A mold transport assembly is provided for moving the mold carriage from a pouring position within the mold tunnel to a loading position located outside of the mold tunnel. An evacuation system is connected to the melt chamber, the charging chamber and the mold tunnel for producing a vacuum therein.
In a preferred embodiment, the melt chamber is provided with a fixed side wall and a movable side wall which is detachably connected to the fixed side wall. A furnace transport assembly is connected to the movable side wall and to the induction furnace. The furnace transport assembly makes it possible to move to the side wall and the furnace laterally until the furnace is removed from the melt chamber. By having a side opening melt chamber, the furnace can be much more readily removed from the melt chamber than in prior conventional configurations where the top of the melt chamber must be removed and the furnace lifted from the melt chamber.
In a more specific aspect, the furnace transport assembly includes laterally extending rails which are positioned for receiving and supporting the movable side wall and the induction furnace. The rails include a pair of narrow gauge fixed rail segments located within the melt chamber for supporting the furnace when the furnace is located within the melt chamber. In addition, a pair of wide gauge fixed rail segments are located at a lateral location distal from the melt chamber. A pair of movable rail segments are located proximal to the melt chamber and a rail adjustment mechanism is provided for adjusting the spacing of the movable rail segments from a wide gauge corresponding to the gauge of the wide gauge fixed rail segments and to the a narrow gauge corresponding to a pair of narrow gauge fixed rail segments located within the melt chamber for supporting the furnace when it is located within the melt chamber.
In a further aspect, the melting system includes a launder chamber which is communicatively connected to the melt chamber and having a door providing access to the launder chamber, and also including a launder adapted for receiving molten metal from the furnace. An isolation valve is located between the melt chamber and the launder chamber and is movable between opened and closed positions, the closed position isolating the launder chamber from the melt chamber to permit positioning of the launder in a loading position within the launder chamber through said door thereof, and the open position providing communication between the launder chamber and the melt chamber to permit moving the launder to a pour position within the melt chamber. A launder transport assembly cooperates with the launder for moving the launder from a loading position within the launder chamber to a pour position within the melt chamber where it is positioned for receiving molten metal poured from the furnace and for discharging the molten metal through the pour opening into the mold tunnel.